Для строк нужна вот такая магия
Код:
W:String;
L:Integer;
w:=Edit1.Text;
L:=Length(W);
stream := TFileStream.Create('qwe.my', fmCreate);
stream.Write(L,SizeOf(L));//<<==-------
stream.write(W[1],L*Siseof(W[1]));//<<==-------
Stream.Free;
.........................................
stream := TFileStream.Create('qwe.my', fmOpenRead);
stream.Read(L,SizeOf(L));//<<==-------
SetLength(W,L);//<<==-------
stream.Read(W[1],L*Siseof(W[1]));//<<==-------
Stream.Free;
ShowMessage(w);